An absorbent and an absorptive article including the absorbent such as disposable diapers, sanitary products, medical blood absorbing articles, and pet care goods are used for the purpose of treating body fluids or excreta, and required to have excellent absorbability. The absorbent and absorptive article including the absorbent have been researched so as to achieve reductions in the weight and thickness of the article. Furthermore, from the viewpoint of environmental consideration or from the aspect of good hygiene, there has been studied water-disintegrable and biodegradable products which can achieve a reductions in an incineration amount and can be flushed down a toilet after use.
An acrylic acid-based absorbent material made of a synthetic resin which can absorb water in an amount from several tens to several thousands times of its own weight is known as an absorbent material serving as an absorbent. In particular, a product obtained by dispersing particles of a high water-absorption resin made of a polyacrylate-crosslinked product in a pulp fiber is widely used. In the case of the acrylic acid-based absorbent material, a liquid or fluid substance such as a body fluid or excreta is absorbed and retained and fixed in the material only after the liquid or fluid substance arrives at the position existing the absorbent material. Therefore, it takes time to bring all of the liquid or fluid substance to the position, and the liquid leakage may be occurred until the liquid arrives at the position.
Though the acrylic acid absorbent exhibits a very large absorbing amount for ion-exchange water, the amount is largely lowered for ion-containing liquid such as a body fluid. In order to enhance the absorbability, an attempt to lower a crosslinking degree has been made, but the attempt lowers the gel strength, which is quite problematic in practical use.
Until now, an absorbent including a polysaccharide has been studied as an absorbent including no acrylic acid-based absorbent material. For example, there has been proposed a film-like water absorbent material formed by crosslinking a cellulose derivative or a salt thereof with a crosslinking agent, in which the amount of water absorption to 0.9% physiological saline is 10 times or more its own weight, and the gel strength in a state where the aqueous solution is absorbed twenty times its own weight is 3,000×10−7N/mm2 or more, and an absorptive article including the film-like water absorbent material (Patent document 1). In addition, there has been also proposed a biodegradable and high-absorbent resin composition obtained by mixing sodium alginate, a carboxylated derivative thereof, or a mixture thereof with a synthetic polymer electrolyte at a weight ratio of 20:80 to 99:1 (Patent document 2). Furthermore, there has been proposed an article for thickening body fluids or excreta which contains a polysaccharide capable of being thickened in the presence of a polyvalent metal ion, the polysaccharide being present in a state ready to dissolve or be dissociated in the aqueous component in body fluids or excreta (Patent document 3).
However, in the film-like water absorbent material and water absorptive article containing the material disclosed in Patent document 1, a crosslink is formed with a crosslinking agent before use same as in the case of a conventional granular high water-absorbent resin, and the crosslink thus lowers the amount of water absorbed in the material. Therefore, it is necessary to use a large amount of the absorbent material for keeping the amount of water absorbed in the product, resulting in increases in the mass/thickness of the absorbent although the material and article are film-like products. In addition, as the film-like absorbent is a cellulose derivative, there are problems that it is difficult to obtain electrostatic repulsion in the polymer chain and adsorption is slow compared to a general high water-absorbent resin.
The biodegradable and high absorbent resin composition obtained by mixing sodium alginate, a carboxylated derivative of sodium alginate, or a mixture thereof with a synthetic polyelectrolyte, disclosed in Patent document 2, comprises sodium alginate (carboxylated derivative) and the synthetic polyelectrolyte. Therefore, the absorption amount of the material is lowered by crosslink as described above. Accordingly, it is necessary to use a large amount of an absorbent material for keeping the absorption amount of the product, resulting in increases in the mass/thickness of the absorbent. In addition, there are problems in that static electricity repulsion in the polymer chain is hardly obtained and absorption is slow compared to a general high water-absorbent resin.
The article for thickening body fluids or excreta disclosed in Patent document 3 includes a polysaccharide that is dissolved in the aqueous component in excreta and is capable of being thickened in the presence of a polyvalent metal ion. However, the source of the polyvalent metal ion is only the body fluids or excreta, and the article does not include a source of the polyvalent metal ion. Only the metal ion in excreta cannot provide enough thickening effect, and the article cannot absorb and retain the liquid in a sufficient amount.
[Patent document 1] JP-A-2006-192368
[Patent document 2] JP-A-H06-306298
[Patent document 3] JP-A-2000-201976